Color Vision

Abstract

Color, like pitch in music, is a perceived quality. Just as pitch depends upon the frequency of a tone, color depends strongly on the frequency (or wavelength) of the light that reaches our eyes.

Color does not occur in the world, but in the mind.

—Diane Ackerman

Glossary of Terms

adaptation

Adjustment of rod and cone sensitivities to deal with different light levels.

afterimage

Image that occurs after a stimulus is removed. Afterimages may be either positive (same color) or negative (complementary color).

brightness

Sensation of overall intensity, ranging from dark, through dim, to bright.

chroma

Color intensity; a term used by artists to mean something similar to saturation .

chromatic lateral inhibition

Ability of one part of the retina to inhibit color perception at another part.

chromaticity diagram

A diagram on which any point represents the relative amount of each primary color needed to match any part of the spectrum.

chromostereopsis

A visual illusion whereby the impression of depth is conveyed in two-dimensional color images, usually of red–blue or red–green colors.

color constancy

Objects tend to retain the same perceived color even though the coloration of the illumination may change.

color tree

A diagram whose vertical axis represents lightness , the distance from the axis represents saturation , and the angle represents hue.

complementary colors (of light)

Two colors that produce white light when added together.

complementary colors (of pigment)

Two colors that produce black when added together.

cone

Photoreceptor that is sensitive to high light levels and differentiates between colors.

deuteranopia

Color blindness resulting from insensitivity to green light.

fovea

Area at the center of the retina that consists almost entirely of cones.

hue

Color name; what distinguishes one color from another.

Ishihara Color Test

A common test used to diagnose color deficiency.

luminance

Term used in the Ostwald color classification system; similar to brightness.

monochromacy

The lack of ability to distinguish colors.

Munsell color system

A color system using ten basic hues, each of which has ten gradations, Chroma scales are of different lengths, depending on the particular hue and value .

opponent-process theory

Receptors transmit information about color pairs (blue–yellow, green–red, or black–white) by increasing or decreasing neural activity.

Ostwald color system

A color system that uses the variables of dominant wavelength , purity , and luminance . Colors are arranged so that hues of maximum purity form an equatorial circle with complementary colors opposite.

photopic

Conditions of high light level under which cone vision predominates.

primary colors (additive, of light)

Three colors that can produce white light .

primary colors (subtractive, of filters or pigments)

Three colors that can produce black.

protanopia

Color blindness resulting from insensitivity to red light .

purity

A term used in the Munsell color system; similar to saturation .

Purkinje shift

At high light levels a red object may appear brighter than a blue object, but at low light levels the same blue object may appear brighter than the red one.

purple line

The straight line connecting the violet and red ends of the CIE diagram.

retinex theory

Theory originated by Edwin Land; receptors in three retinex systems are sensitive to long-, medium-, and short-wavelength light.

rhodopsin

Photosensitive material in rods and cones.

rods

Photoreceptor that is sensitive to low light levels but does not differentiate colors.

saturation

Purity of a color; spectral colors have the greatest saturation ; white light is unsaturated.

scotopic

Conditions of low light level under which rod vision predominates.

value

A term meaning brightness.